//设置cookie
function setCookie(cname, cvalue, exdays) {
    var d = new Date();
    d.setTime(d.getTime() + (exdays*24*60*60*1000));
    var expires = "expires="+d.toUTCString();
    document.cookie = cname + "=" + cvalue + "; " + expires+"; path=/";
}
//获取cookie
function getCookie(cname) {
    var name = cname + "=";
    var ca = document.cookie.split(';');
    for(var i=0; i<ca.length; i++) {
        var c = ca[i];
        while (c.charAt(0)==' ') c = c.substring(1);
        if (c.indexOf(name) != -1) return c.substring(name.length, c.length);
    }
    return "";
}
//清除cookie  
function clearCookie(name) {  
    var keys=document.cookie.match(/[^ =;]+(?=\=)/g); 
    if (keys) { 
    for (var i = keys.length; i--;) 
    document.cookie=keys[i]+'=0;expires=' + new Date( 0).toUTCString() 
    }   
}  